1. Field of the Invention
This invention relates in general to radiation therapy, and, more particularly, to an apparatus, for use in combination with a diagnostic computer tomography (CT) scanner that uses a radiant energy beam for imaging purposes, for permitting the therapeutical irradiation of a chosen area with the radiant energy beam.
2. Description of the Related Art
Prior use of the diagnostic computer scanner limited the use of its radiant energy beam to imaging purposes. A patient was placed within the scanner gantry and sequential scanning of the patient commenced using the radiant energy beam of the scanner to provide a series of images representing the internal structure of the patient without the need for intrusive surgery.
If the images derived from the scanning procedure indicated that radiation therapy of a particular area of the patient was desirable, several possibilities were available. In any event, however, in each of these possibilities the patient was normally removed from the scanner upon conclusion of the scanning procedure and radiation therapy was performed upon a second apparatus designed specifically for radiation therapy procedures.
The reason a second apparatus is normally employed is due to the fact that the radiation energy levels necessary for radiation therapy are incompatible with those levels used in scanning a patient. Radiation therapy calls for radiation energy levels capable of destroying target tissue, while scanning for imaging purposes uses radiation energy levels held at a much lower level to prevent the destruction of tissue during the scanning and imaging procedure itself. Thus, many consider the two procedures to be incompatible upon the same apparatus.
The use of two devices results in physical difficulties in successfully re-positioning the patient and locating the position and extent of the target area to be therapeutically irradiated. This fact, along with the additional fact that physical changes may have occurred to the patient during the time interval between the imaging and therapy procedures, all cause considerable problems in guarantying a successful procedure for the patient at a minimum of danger and discomfort.
The present invention overcomes not only these problems, but does so at a considerable lessening of the danger and risk to the patient undergoing such radiation therapy.
The present invention can be used in combination with existing diagnostic computer tomography scanners, thus enabling an existing apparatus, presently in widespread use, to add a therapeutic dimension to its purpose at little modification and small cost. Radiation therapy may therefore be provided by medical centers previously unable to do so due to the expense of purchasing, installing and operating a separate radiation therapy device.
In addition, the present invention provides a number of benefits over existing radiation therapy devices.
Specifically, in comparison with a gamma knife radiation therapy device, the present invention provides a more flexible geometry, and thus a more flexible irradiated target volume size and shape for radiation purposes. Likewise, since the present invention can be used in combination with existing computer tomography scanners, it has a lower cost and weight than the gamma knife. Unlike the gamma knife, the present invention provides a diagnostic imaging capability, and the lower x-ray energy used in the present invention utilizing a scanner unit allows for iodine dose enhancement of the target area. Also imaging of the patient may occur contemporaneous with the radiation therapy procedure, thus allowing real time monitoring the position of the target area chosen for irradiation. Thus the present invention provides for more accurate localization of the area to be irradiated than prior art use of the gamma knife as a standalone radiation therapy unit. The present invention also does not require any stereotactic device for more precise positioning than that of the gamma knife. Finally, the present invention uses a lower x-ray energy level that allows a higher RBE, thus lessening the total dose requirement needed for successful radiation treatment and improving the dose profile due to the continuous rotation and increased number of radiation fields provided by utilization of a scanner unit that are not found in the gamma knife presently in use for radiation therapy procedures.
Another apparatus currently in use for radiation therapy procedures is the radiation therapy unit using either cobalt, a linear accelerator or orthovoltage to produce its radiant energy beam.
Likewise, over the radiation therapy unit, the present invention provides for stereotactic localization and more accurate positioning of the patient due to the fact that a single device having diagnostic imaging capability is used for both imaging and therapy purposes, The present invention thus eliminates the need for patient movement and repositioning by providing for real time patient imaging contemporaneous with the radiation therapy for monitoring the target area location and position with respect to the radiation beam.
The present invention also provides for a more flexible geometry for the chosen target area. The present invention is also found in a device that has a lower cost and weight than the radiation therapy units in common use today.
Another positive aspect of the present invention over that of existing radiation therapy units is that the x-ray tube used in most computer tomography scanners provides a higher dose rate than either cobalt or other isotopic sources of radiant energy. The present invention also provides for more accurate localization of the effects of the radiant energy beam, while the lower x-ray energy level allows for iodine dose enhancement of the target area and a higher RBE, thereby lessening the total radiation dose requirement. The CT scanner gantry tilt capability of the present invention is much more flexible geometrically than available with linear accelerators used for radiation therapy. Finally, the present invention provides for an improved radiation dose profile over that of radiation therapy units due to a continuous rotation of an increased number of fields providing the radiation beam.
The prior art includes the use of variable collimators for radiation therapy, but not in connection with diagnostic CT scanners as in the present invention.